1. Field of the Invention
The present invention relates to an abrasion resistant coated fiber structure having an excellent resistance to flexural fatigue and a superior flame retardant resistance. More particularly, the present invention relates to an abrasion resistant coated fiber structure in the form of, for example, a belt, cord, rope, thread, woven or knitted fabric or felt (nonwoven fabric), having specific abrasion resistant coating layers formed on surfaces of individual fibers in the structure and exhibiting an excellent resistance to abrasion and flexural fatigue, and a flame retardant resistance.
2. Description of the Related Arts
It is known that fibrous materials usable for forming belts, cords, ropes threads, woven and knitted fabrics or felts (non-woven fabrics) having a satisfactory wear durability, comprise at least one type of fibers selected from polyester fibers, polyamide fibers, water-insolubilized polyvinyl alcohol fibers, wholly aromatic polyamide (aramide) fibers, wholly aromatic polyester fibers, ultra-high molecular weight polyethylene fibers, and optionally for special uses, glass fibers and carbon fibers.
Sometimes, the above-mentioned fibers can be directly converted to a desired fiber structure without applying a surface treatment to the fibers, but in general, to provide a fiber structure having a specific property, the fibers are formed into yarns and the resultant yarns are surface treated with a specific treating material which will effectively impart the specific property to the fibers, before the yarns are converted to the fiber structure. Alternatively, the fibers are directly converted to a precursory fiber structure, followed by applying a specific treatment to the precursory fiber structure to impart a specific property to the surfaces of the fibers.
Also, in general, the fiber structures having a satisfactory wear durability, and thus usable for various purposes, must exhibit, in addition to a high resistance to abrasion, an excellent flexural fatigue and a superior flame retardant resistance.
To satisfy the above mentioned requirements, the fiber structures are treated or impregnated with a treating material so that the surfaces of individual fibers in the fiber structures are covered with a specific surface-coating material.
The surface-coating material for the fibers can be usually selected from, for example, conventional polyurethane resins and silicone resins, the resultant treated fiber structures are utilized for various purposes.
For example, Japanese Examined Patent Publication (Kokoku) No. 62-60511 discloses a fibrous rope in which individual fibers are coated with a mixture of a polyurethane resin, polyethylene oxide, and ethylene-urea compound. Also, Japanese Unexamined Patent Publication (Kokai) No. 60-173,174 discloses a method of enhancing an abrasion resistance of a fibrous belt, in which method a resinous treating material comprising, as a main component, a blocked urethane prepolymer, is applied to a precursory fibrous belt and then heat treated. Further, Japanese Examined Patent Publication No. 1-29909 discloses a method of producing a treated fiber structure by treating a precursory fiber structure with a first treating liquid comprising, as a main compound, a silane type coupling agent, and then with a second treating liquid comprising, as a main component, an ethyleneurea compound.
The above-mentioned treating materials do effectively enhance the abrasion resistance of the fiber structure surface treated or impregnated therewith, but due to recent rapid advances in the uses of the fiber structures in many fields, the properties of the fiber structures must be further enhanced to a higher level. Therefore, the above-mentioned treated or impregnated fiber structures do not always have satisfactory specific properties, for example, abrasion resistance and flexural fatigue resistance.
For example, the conventional para-type aramide fibers have a very high tensile strength of 20 g/d or more, and thus are now widely used when forming various fiber structures for example, belts, cords or ropes. But the para-type aramide fibers are disadvantageous in that, when rubbed together or against a metal article, the fibers are fibrilized and exhibit a lower mechanical strength due to the fibrilization, and thus cannot exhibit the inherent high mechanical strength of the fiber structure.
To overcome the above-mentioned disadvantage, an attempt has been made to provide a fiber structure, for example, belt, cord, rope or felt, having a core portion formed from aramide fibers and surface portions thereof formed from conventional polyamide (nylon 6 or 66) fibers. The resultant composite fiber structure is now in practical use but does not always exhibit satisfactory properties. Especially, the fibrilization of the aramide fibers is not sufficiently prevented by the above-mentioned composite structure. Further, when the composite structure is stretched under a load during practical use, the load is borne only by the core portion thereof having less elongation than the surface portion. For example, the practical mechanical strength of a rope or cord having the above-mentioned composite structure is similar to that of the core portion thereof. Further, when repeatedly flexed (bent), the aramide fibers in the core portion of the composite structure are rubbed together and fibrilized, and thus the mechanical strength thereof cannot be maintained at a high level for a long time.
Recently, when used in the electric and electronic industries, the various fiber structures must have a high flame retardant resistance. Usually, a conventional treating material causes a reduction in the flame retardant resistance of the aramide fibers, and therefore, a conventional surface treated or aramide fiber structure impregnated with the treating material exhibits a lower flame retardant resistance than that of a non-treated aramide fiber structure.
Also, in the composite structure, the surface portion thereof is formed of the conventional organic fibers having a lower flame retardant resistance than that of the aramide fibers, and thus the composite structure exhibits a unsatisfactory flame retardant resistance.